For service and parts needs, visit your dealer. You will receive genuine GM parts and GM-trained and supported service people.
Genuine GM parts have one of these marks:

Vehicle Care
California Proposition 65 WarningRear Compartment Lid Replacement
Preliminary Procedure
Remove the rear compartment lid inner panel trim. Refer to Rear Compartment
Lid Inner Panel Trim Replacement.
Rear Compartment Lid Hinge Bolt (Qty: 4)
Caution: Refer to Fastener Caution in the Preface section.
Tighten
9 N·m (80 lb ft)
Rear Compartment Lid
...
Headlamp Aiming Procedure
Open the hood.
Measure from the floor to the center of the headlamp bulb. Some
headlamps have an aim dot marked on the headlamp lens.
At the screen, measure from the floor and place the horizontal tape at
the measured distance.
Measure from the reference line on the floor to the le ...
Installation Procedure
Align the rocker inner panel.
Drill 8 mm (5/16 in) for plug welding along the edges of the quarter
outer panel as noted from the original panel.
Clean and prepare the attaching surfaces for welding.
Position the rocker inner panel on the vehicle.
Verify the fit of ...